Cross-flow wind turbine

ABSTRACT

Disclosed are various embodiments of cross-wind turbines that are capable of providing high efficiencies over a wide range of wind velocities. An airfoil stator causes wind to accelerate along its surface and creates a low pressure area on the leading face of the rotor blade during the power stroke. A blocking stator blocks wind from impeding the movement of the rotor blades during the return cycle and directs wind onto the trailing face of the rotor blades during the power cycle. A large pressure differential is created between the leading face of the rotor blade and the trailing face of the rotor blade during the power cycle which creates a large amount of force that rotates the rotor blade about the central shaft. In some embodiments, gaps are provided between the inside edge of the rotor blade and a stationary shaft which vents wind collected by the rotor blade during certain portions of the rotation cycle. The vented wind increases the pressure on the trailing face of the rotor blades during the return cycle to further assist in the efficiency of this system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/284,774, entitled “Cross-Flow Wind Turbine,” filed Nov. 21, 2005,which is a continuation-in-part of U.S. patent application Ser. No.10/831,515 entitled “Wind Turbine Having Airfoils for Blocking andDirecting Wind and Rotors With or Without a Central Gap” by RonaldTaylor and Scott Taylor, filed Apr. 23, 2004, which claims the benefitof and priority to U.S. Provisional Patent Application Ser. No.60/467,773 entitled “Wind Turbine” by Ronald Taylor and Scott Taylor,filed Apr. 30, 2003. U.S. patent application Ser. No. 11/284,774 furtherclaims the benefit of U.S. Provisional Patent Application Ser. No.60/639,448, filed on Dec. 23, 2004, entitled “Cross-Flow Wind Turbine.”The entire contents of the above mentioned applications are herebyspecifically incorporated herein by reference for all they disclose andteach.

BACKGROUND OF THE INVENTION

Wind turbines have provided a valuable source of alternative energy.Constant improvements in wind turbine systems have been made over thepast few years. Most of the wind turbine systems in use today areaxial-flow systems that are otherwise known as propeller systems. Inaxial-flow wind turbine systems, air travels in a direction that issubstantially parallel to the rotating axis of the wind turbine. Thelarge propeller blades are driven by the wind at a rotational speed thatcreates tip speeds of the blade that can range from approximately six tonine times the speed of the wind. Tip speeds of over several hundredmiles an hour can be achieved in moderately strong to strong winds whichwill cause axial-flow wind turbines to break apart. Hence, expensivebraking systems and systems for feathering the angle of the blades mustbe used to control the speed of axial-flow wind turbines in moderatelystrong to strong winds. As a result, axial-flow wind turbines areinefficient in moderately strong to strong winds and, as such, areunable to extract power from wind energy when it is at its greatestenergy producing level. In effect, axial-flow wind turbines are designedfor use in light to moderate winds.

Further, axial-flow wind turbines are very dangerous to birds. Birds arefrequently killed by the inability of these avians to sense the presenceof the rapidly moving blades of the axial-flow wind turbines.

Cross-flow wind turbines constitute a different class of wind turbines.See U.S. patent application Ser. No. 10/831,515, entitled “Wind TurbineHaving Airfoils for Blocking and Directing Wind and Rotors With orWithout a Central Gap,” filed Apr. 23, 2004, and U.S. Pat. No.6,015,258, entitled “Wind Turbine,” issued Jan. 18, 2000, the entirecontents of which is hereby incorporated herein by reference for all itdiscloses and teaches. In cross-flow wind turbines, the wind flowsacross the rotors in a direction that is substantially normal to theaxis of the rotating shaft. Cross-flow wind turbines have certainadvantages over axial-flow wind turbines, but have not previously beenseriously considered as a source of alternative energy because of thecomparatively lower efficiencies with respect to the axial-flow windturbines. An advantage of the cross-flow wind turbine is that the tipspeed of the rotors of the cross-flow wind turbines move at a maximumspeed that is only slightly greater than the speed of the wind. As such,cross-flow turbines can operate equally as well in both low and highwind conditions. In addition, the cross-flow wind turbine is easily seenby birds resulting in no avian deaths. Cross-flow wind turbines are alsomuch quieter than the axial-flow wind turbines, primarily because thecross-flow wind turbines do not move at a high rate of speed and do notcreate a substantial amount of turbulence.

SUMMARY OF THE INVENTION

An embodiment of the present invention may therefore comprise a methodof capturing wind energy using a cross-flow wind turbine comprising:generating a low pressure area on a leading face of a rotor blade byaccelerating the flow of air across the surface of an airfoil statorthat is positioned to form a predetermined gap between the rotor bladeand the air foil stator during a power stroke of the rotor blade; usinga blocking stator to substantially block wind from impeding movement ofthe rotor blade during a return cycle of the rotor blade and directingthe substantially blocked wind to a trailing face of the rotor duringthe power stroke of the rotor blade so as to create a pressuredifferential between the leading face and the rotor blade and thetrailing face of the rotor blade during the power stroke that creates aforce that rotates the rotor blade.

An embodiment of the present invention may further comprise a cross-flowwind turbine system that is capable of capturing wind energy comprising:a rotor having at least two semicircular shaped rotor blades; an airfoilstator positioned to capture and accelerate wind across an airfoilsurface of the airfoil stator and provide a gap having a predeterminedsize between the rotor blades and the airfoil surface so that a negativepressure area is formed on a leading face of the rotor blades as therotor blades pass by the airfoil surface during a power stroke; and ablocking stator positioned to substantially block wind from impedingupon the leading face of the rotor blades during a return stroke anddirect wind that is blocked by the blocking stator onto a trailing faceof the rotor blades during the power stroke such that a pressuredifferential is created between the leading face of the rotor blades andthe trailing face of the rotor blades during the power stroke thatcreates a force that rotates the rotor blade.

An embodiment of the present invention may further comprise a cross-flowwind turbine that generates mechanical energy from wind comprising: arotor having a plurality of rotor blades that are substantiallysymmetrically disposed around a rotor; a rotor space formed in a volumethat is swept out by the rotor blades, the rotor space having a driveportion in which the rotor blades are driven by the wind and a returnportion in which the rotor blades return to the drive portion; aplurality of stators that direct wind into the drive portion and directwind away from the return portion to cause the rotor to turn andgenerate the mechanical energy, the stators being placed around therotor to provide a substantially bidirectional cross-flow turbine.

An embodiment of the present invention may further comprise a method ofgenerating mechanical energy from wind comprising: providing across-flow wind turbine having stators and a rotor that sweeps out arotor space, the rotor space having a drive portion and a returnportion; placing a plurality of rotor blades substantially symmetricallyaround the rotor; placing the stators around the rotor in locations thatsubstantially direct the wind into the drive portion of the rotor spaceso that the wind drives the rotor blades in the drive portion, andsubstantially block the wind from entering the return portion of therotor space so that the rotor blades return to the drive portion togenerate the mechanical energy.

An embodiment of the present invention may further comprise a method ofcapturing wind energy using a cross-flow wind turbine comprising:providing an airfoil stator that is positioned to capture and acceleratewind across an airfoil surface of said airfoil stator; generating a lowpressure area on a leading face of a rotor blade by positioning theairfoil stator to form a predetermined gap between the rotor blade andthe airfoil stator, the low pressure area generating a force on theleading face of the rotor blade that rotates the rotor blade in anefficient manner.

An embodiment of the present invention may further comprise a cross-flowwind turbine system that is capable of capturing wind energy comprising:a rotor having at least two semicircular shaped rotor blades; an airfoilstator positioned to capture and accelerate wind across an airfoilsurface of the airfoil stator and provide a gap having a predeterminedsize between the rotor blades and the airfoil surface so that a negativepressure area is formed on a leading face of the rotor blades as therotor blades pass by the airfoil surface that creates a force thatrotates the rotor blades.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1A is a top schematic view of one embodiment of the invention.

FIG. 1B provides typical dimensions of the embodiment of FIG. 1A.

FIG. 2 is a schematic illustration of another embodiment of theinvention.

FIG. 3 is an efficiency graph illustrating efficiencies of theembodiment of FIG. 1A based on wind direction.

FIG. 4A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 1A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 4B is an efficiency graph of the embodiment of FIG. 4A.

FIG. 5 is a wind velocity and directional flow diagram of the embodimentof FIG. 4A.

FIG. 6A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 6A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 6B is an efficiency graph of the embodiment of FIG. 6A.

FIG. 7 is a wind velocity and directional flow diagram of the embodimentof FIG. 6A.

FIG. 8A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 8A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 8B is an efficiency graph of the embodiment of FIG. 8A.

FIG. 9 is a wind velocity and directional flow diagram of the embodimentof FIG. 8A.

FIG. 10A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 10A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 10B is an efficiency graph of the embodiment of FIG. 10A.

FIG. 11 is a wind velocity and directional flow diagram of theembodiment in FIG. 10A.

FIG. 12A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 12A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 12B is an efficiency graph of the embodiment of FIG. 12A.

FIG. 13 is a wind velocity and directional flow diagram of theembodiment of FIG. 12A.

FIG. 14A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 14A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 14B is an efficiency graph of the device of FIG. 14A.

FIG. 15 is a wind velocity and directional flow diagram of theembodiment of FIG. 14A.

FIG. 16A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 16A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 16B is an efficiency graph of the embodiment of FIG. 16A.

FIG. 17 is a wind velocity and directional flow diagram of the device ofFIG. 16A.

FIG. 18A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 18A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 18B is an efficiency graph of the embodiment illustrated in FIG.18A.

FIG. 19 is a wind velocity and directional flow diagram of theembodiment illustrated in FIG. 18A.

FIG. 20A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 20A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 20B is an efficiency graph of the embodiment illustrated in FIG.20A.

FIG. 21 is a wind velocity and directional flow diagram of theembodiment illustrated in FIG. 20A.

FIG. 22A is an illustration of pressure gradients that are produced bythe embodiment of FIG. 22A as calculated from computer simulations usingcomputational fluid dynamics.

FIG. 22B is an efficiency graph of the embodiment of FIG. 22A.

FIG. 23 is a wind velocity and directional flow diagram of theembodiment of FIG. 22A.

FIG. 24 is a schematic illustration of the manner in which theembodiment of FIG. 1A can be constructed.

FIG. 25 is an isometric view of the embodiment of FIG. 1A.

FIG. 26 is an isometric view of the embodiment of FIG. 1A viewed from adifferent orientation.

FIG. 27 is an isometric view of the rotor of the embodiment of FIG. 1A.

FIG. 28 is a schematic illustration that shows one manner of couplingthe shaft of the rotor to a generator.

FIG. 29 is a schematic illustration that shows another manner ofcoupling the shaft to the generator.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A is an illustration of one embodiment of a cross-flow windturbine 100. The cross-flow wind turbine includes an air foil stator 102that is fixed, stator 104 that is fixed and stator 106 that is alsofixed. The rotor 108 rotates in response to forces created by wind.Rotor 108 includes rotor blade 110, rotor blade 112 and a rotating shaft114. The cross-flow wind turbine 100, illustrated in FIG. 1A, isdesigned for maximum efficiency for wind flowing in a primary direction116 which may be aligned with the prevailing wind at a specificgeographical location. However, the cross wind flow turbine 100 alsoproduces high efficiencies for winds flowing from other directions, asdescribed in more detail below with respect to FIG. 3.

As also shown in FIG. 1A, the angular positions of the stators are shownwith respect to the primary wind flow direction 116. The cross-flow windturbine 100 that is illustrated in FIG. 1A shows each of the elementsgenerally in their relative proportional sizes with respect to eachother. It is believed that scaling of the cross-flow wind turbine 100will not change the relative proportional sizes of the various elementsor their location with respect to each other. It is anticipated that asthe cross-flow wind turbine 100 is scaled to larger sizes that Reynoldsnumbers and differences in flow characteristics on larger scales willresult in higher efficiencies as compared to wind tunnel testing of thecross-flow wind turbine 100. Rotor blade 110 and rotor blade 112 areattached to the shaft 114 so that as the rotor blades 110, 112 are movedby the wind, shaft 114 rotates. Rotor blades 110, 112, as illustrated inFIG. 1A, have shapes that are circular arcs of 120°. Empirical datagathered from both wind tunnel testing and computational fluid dynamicsindicate that the 120° circular arc shape of rotor blades provides thehighest efficiency.

The air foil stator 102 that is shown in FIG. 1A has a cambered profilethat acts like an airplane wing so that air flowing across surface 118of air foil stator 102 is accelerated. The accelerated flow of airacross surface 118 creates a low pressure region on the leading face 120of rotor blade 110 which helps to pull the rotor blade 110 through itspower stroke. Because the wind flowing in the primary wind flowdirection 116 is pushing on the trailing face 122 of rotor blade 110, alarge pressure differential exists between the trailing face 122 and theleading face 120 of rotor blade 110. This large pressure differentialassists the rotor blade 110 in moving in a counterclockwise directionaround the shaft 114. The pressure gradients created are disclosed inmore detail in FIG. 4A. Stator 104 is positioned to block wind, flowingfrom the primary wind flow direction 116, from impinging upon theleading face of the rotor blades during the return cycle, which isillustrated by the position of the rotor blade 112 in FIG. 1A. Stator104 not only blocks wind from hitting the rotor blades during the returncycle, but also redirects the wind flowing from direction 116 to impingeupon the trailing face 122 of the rotor blade 110.

Stator 106 of FIG. 1A functions to guide the air flow on the downwindside of the rotor 108 away from the cross-flow wind turbine 100. Stator106 also provides a third leg of a tripod structure to add structuralrigidity to the system. Stator 106 also can perform other valuablefunctions. Wind flow studies for many geographical locations haveprovided data that the prevailing wind flows from a predominantdirection during the windy season, which may, for example, be Winterseason at many geographical sites. During the opposite season(off-season), such as Summer, the wind typically comes from asubstantially opposite direction. Although the wind flow in theoff-season may be only a fraction of the wind flow from the primaryseason, it still may be advantageous to capture the off-season wind withsome degree of efficiency and convert it to mechanical energy. As can beseen from FIG. 1A, stator 106 can assist in redirecting wind into rotorblade 112 when the wind is from a direction 130 that is opposite to theprimary wind flow direction 116. In that regard, it may also bedesirable in some embodiments to provide camber to the stator 106 sothat it creates an air foil, in a manner similar to the air flow stator102. However, the primary purpose of the stator 106 is to providestructural rigidity and to assist the flow of wind in exiting theturbine without creating back pressure that would impede the performanceof the cross-flow wind turbine 100.

Of course, to provide structural rigidity, stator 106 could be replacedwith simply a structural member. Depending on the wind studies of aparticular area, replacement of stator 106 with a structural member maymake sense if the wind flow direction is almost exclusively fromdirection 116. Wind flow from direction 132 would allow stator 106 tofunction in a manner similar to stator 104, i.e., stator 106 would blockwind from direction 132 during the return cycle of the rotor blades andredirect the wind to the trailing face of the rotor blades during thepower stroke. Hence, if off-season wind comes from direction 132, asshown in FIG. 1A, stator 106 may provide advantageous properties for thecross-flow wind turbine 100.

Collected wind data from wind studies at a large majority ofgeographical sites have shown that a very large percentage (up to 90% ormore) of the wind comes from the same quadrant as the prevailing winddirection. These studies have also shown that winds during theoff-season are usually from the opposite quadrant, as indicated above.For example, if the primary wind flow direction 116 is the primary winddirection during the windy season, wind typically flows from direction130 during the off season, at most geographical sites. However, theoff-season winds carry only a fraction of the energy that is availablefrom the winds in the primary wind flow direction in most geographicalsites. Hence, the system of FIG. 1A is optimized for wind coming fromthe quadrant of the prevailing wind such that the primary flow direction116 is aligned with the prevailing wind flow direction when thecross-flow wind turbine is installed at a site. As discussed in moredetail with respect to FIG. 3, the system shown in FIG. 1A is anomni-directional system which has optimized efficiencies for a primarywind flow direction 116 and reduced efficiencies when the wind flowsfrom a direction other than the primary wind flow direction 116. Again,however, the largest overall efficiency and the best return oninvestment comes from optimization of a system that captures wind fromthe prevailing wind direction for most geographical sites.

The embodiment of FIG. 1A has produced the highest efficiencies of thevarious embodiments disclosed herein for wind tunnel testing. Computersimulations using computational fluid dynamics have shown that theembodiment of FIG. 2 provides the highest efficiencies. Empirical datacollected from live testing of full scale systems will provide the bestdata as to which embodiment provides the highest efficiencies.

FIG. 1B provides a list of dimensions for both a 10 kilowatt cross-flowwind turbine having a total height of 33 feet and 1000 kilowatt turbinehaving a total height of 230 feet for the embodiment of FIG. 1A. Again,it is believed that the dimensions of these devices scale linearly withsize.

FIG. 2 illustrates another embodiment 200 of a cross-flow wind turbine.The embodiment of FIG. 2 utilizes a stationary shaft 202. The shaft 202remains stationary as the rotor blades 204, 206 rotate around the shaft202. As can be seen from FIG. 2, stationary shaft 202 has a recessedportion which causes a gap 208 to form between the end of the rotorblade 206 adjacent to the shaft and the recessed portion of the shaft.Hence, a gap opens up between the inside end of the rotor and the shaftduring certain portions of the cycle which causes deventing of the windcaptured by the rotor blades during the power stroke. The wind that isvented through the gap 208 is directed towards rotor blade 206 to assistrotor blade 206 in moving through the return cycle. This is disclosed inmore detail below. In other words, wind captured by the trailing face212 of the rotor blade 204 is directed through the gap 208 and flowsonto the trailing face 210 of the rotor blade 206 to create positivepressure on the trailing face 210.

FIG. 3 is a graph illustrating efficiencies of the cross-flow windturbine 100 that is illustrated in FIG. 1A, versus the direction of windflow. As can be seen from FIG. 3, the highest efficiencies are obtainedfrom wind flowing from directions of approximately 10° to 335°. In thesedirections, efficiencies of 40% to 45% are achieved. When the wind flowsfrom the directions of approximately 210° to 240°, efficiencies rangefrom 35% to 37%. In addition, reasonable efficiencies can be obtained inthe range of 27% to 29% when the wind flows from the direction of 90° to120°. Hence, the cross-flow wind turbine 100 illustrated in FIG. 3 issomewhat omni-directional, but clearly achieves the highest efficienciesof over 40% between 10° and 335°.

FIG. 4A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for cross-flow windturbine 100. The scale 102 shows positive pressures as lighter shadesand negative pressures as darker shades. As can be seen from FIG. 4A,large negative pressures are created on the leading face 120 of rotorblade 110 as rotor blade 110 passes by air foil stator 102 during thepower stroke. The large negative pressures created on the leading face120 of rotor blade 110 result from the accelerated air flow across thesurface of air foil stator 102. These negative pressures function topull the rotor blade 110 in a counterclockwise direction around theshaft. Positive pressure indicated by lighter shades is created on thetrailing face 122 of the rotor blade 110. The large differential inpressure created between the trailing face 122 and the leading face 120of the rotor blade 110 creates a large amount of force on rotor blade110 to cause the rotor blade 110 to rotate in a counterclockwisedirection around the shaft 114. This large amount of force createdduring the power stroke of the cross-flow wind turbine 100 results inhigher efficiencies.

FIG. 4B is an illustration of instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodiment ofFIG. 1A. As can be seen from FIG. 4B, the average efficiency illustratedby plot 402 ranges between 28% and 32%. The plot 404 is theinstantaneous calculated efficiency for the leading face 120 of rotorblade 110 of the embodiment illustrated in FIG. 1A.

The efficiency graphs, such as graph 4B are calculated fromcomputational fluid dynamics simulations on a computer. In thecomputational fluid dynamics simulations, the blades complete a fullrotation every second. The dynamic loads on the blades are shown for onehalf revolution. A half second window shows all of the cyclical forcepatterns as the patterns repeat over the next half revolution with theforces on the blades reversed. Non-dimensional pressure coefficients aremeasured at each time step as the blades rotate through this half cycle.The pressure on the blades is a function of the pressure coefficient andthe reference flow head,

P=C_(p)×q_(ref); where q_(ref) is the reference flow head.

q_(ref)=½p(U_(ref))² where p=air density

-   -   U_(ref)=upstream velocity measured at mid-rotor height        The moments on each blade face, which act to produce energy when        they are positive, are then summed and plotted as the overall        efficiency. The graphs only illustrate a single blade. Hence,        the average efficiency plot 402 is generated from the addition        of efficiencies calculated for both blades. The practical result        is that another set of plots that are 180° out of phase with the        plots shown are added to the plots that are shown in FIG. 4B, as        well as the other efficiency graphs illustrated herein.

The efficiency of the turbine in the wind tunnel and full scale iscalculated from the following formulas:

Power Available in the Wind:P _(w)=½pAS ³ [Watts] P_(w)=power available in the wind

-   -   p=air density, kg/m³    -    =1.225 kg/m³ @ sea level    -   A=rotor swept area, m²    -    =rotor height×rotor diameter    -   S=wind speed, m/s

Turbine Power:P _(t)=Rotor Torque(Nm)×Rotational Velocity (rad/sec) [Watts]

Turbine Efficiency:% Efficiency=(P _(t) /P _(w))×100

Once the turbine's efficiency is determined, the turbine power can alsobe calculated by:P _(t) =P _(w)×efficiency=½pAS ³ ×eff

FIG. 5 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity. As is illustratedin FIG. 5, the wind accelerates in the gap between the air foil stator102 and rotor blade 110 as a result of the air flow characteristics ofthe air foil stator 102 that causes the wind to accelerate on thesurface 118 of airfoil stator 102. The length of the arrows in FIG. 5illustrate the magnitude of the speed of the wind. As shown in FIG. 5,large wind velocities are created along the leading face of the rotorblade 120 which are directed to the trailing face of rotor 112. Thelarge velocities along the surface of the leading face of the rotorblade 110 create a negative pressure while the wind impinging upon thetrailing face of rotor 112 create a positive pressure. In addition,stator 104 directs the wind so that it impinges upon the trailing faceof rotor blade 110.

FIG. 6A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for the cross-flow windturbine 200 that is illustrated in FIG. 2. Scale 602 shows positivepressures as lighter shades and negative pressures as darker shades. Ina manner similar to FIG. 4A, large negative pressures are created on theleading face of rotor blade 204 as the rotor blade 204 passes by the airfoil stator 214 during the power stroke. The large negative pressurescreated on the leading face of rotor blade 204 result from theaccelerated air flow across the surface of air foil stator 214. Thesenegative pressures function to pull the rotor blade 204 in acounter-clockwise direction around the shaft 202. Positive pressureindicated by lighter shades is created on the trailing face of the rotorblade 204. The large differential pressure created between the leadingface and the trailing face of the rotor blade 204 creates a large amountof force on the rotor blade 204 to cause the rotor blade 204 to rotatein a counter-clockwise direction around the shaft 202. This large amountof force created during the power stroke of the cross-flow wind turbine200 results in higher efficiencies. The gap 208 functions to devent thetrailing face of the rotor blade 204, as described above. Wind flowsthrough the gap 208 an impinges upon the trailing face of rotor blade206. This helps to increase the pressure on the trailing face of rotorblade 206 and minimize the effect of any negative pressures on thetrailing face of rotor blade 206 during the return cycle of the rotorblades.

FIG. 6B is an illustration of the instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodiment ofFIG. 2. As can be seen from FIG. 6B the average efficiency illustratedby plot 602 ranges between 33% and 35%. Plot 604 is the instantaneousefficiency of the leading face of the rotor blades of the embodiment ofFIG. 2, while plot 606 illustrates the instantaneous efficiency of thetrailing face of the rotor blades of the embodiment of FIG. 2.

FIG. 7 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity for the embodimentof FIG. 2. As illustrated in FIG. 7, the wind accelerates in the gapbetween the air foil stator 214 and the rotor blade 204 as a result ofthe flow characteristics of the air foil stator 214 that cause the windto accelerate on the surface of the air foil stator 214. The length ofthe arrows in FIG. 7 illustrate the magnitude of the speed of the wind.As also shown in FIG. 7, large wind velocities are created along theleading face of the rotor blade 204 that are directed to the trailingface of rotor blade 206. In addition, wind flowing through the gap 208also impinges on the trailing face of rotor blade 206. FIG. 7 provides agood visual impression of the wind flow characteristics of theembodiment of FIG. 2.

FIG. 8A illustrates the pressure gradients calculated by computersimulations using computational fluid dynamics for the embodiment of thecross-flow wind turbine that is illustrated in FIG. 8A. The embodimentof the cross-flow wind turbine illustrated in FIG. 8A is very similar tothe embodiment illustrated in FIG. 2, with the exception that thestationary shaft 802 is somewhat larger, thereby creating a larger gapduring certain portions of the cycle of rotation. In addition, therotors are slightly shorter. As can be seen from FIG. 8A, the wind flowpatterns create a vortex 804 on the trailing face of rotator blade 806during the return cycle. This vortex is not created in the embodiment ofFIG. 2, as shown in FIG. 6A. As a result, the efficiencies of theembodiment of FIG. 8A are not quite as high as the efficiencies of theembodiment of FIG. 2, as illustrated with more specificity in FIG. 8B.

FIG. 8B is an illustration of instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodimentillustrated in FIG. 8A. As can be seen from FIG. 8B, the averageefficiency illustrated by plot 808 ranges between 27% and 33%. Plot 810illustrates the instantaneous efficiency of the leading face of therotor blades of the embodiment of FIG. 8A, while plot 812 illustratesthe instantaneous efficiency of the trailing face of the rotor blades ofthe embodiment of FIG. 8A.

FIG. 9 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity for the embodimentof FIG. 8A. FIG. 9 illustrates the manner in which large negativepressures are created on the leading face of the rotor blade as a resultof the accelerated air flow on the air foil. FIG. 9 also illustrates themanner in which the vortex is formed from wind flowing between the gapcaused by the recessed portion of the shaft 802 and the rotor blade, aswell as the accelerated wind from the air foil.

FIG. 10A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for the cross-flow windturbine embodiment illustrated in FIG. 10A. The embodiment illustratedin FIG. 10A is similar to the embodiment of FIG. 8A but includes astationary shaft 1002 that is larger than the stationary shaft 802 ofFIG. 8A. As a result, a larger gap 1004 is formed between the rotorblades in the stationary shaft 1002 during certain portions of the cycleof rotation. A vortex 1006 is also created by the embodiment of FIG.10A.

FIG. 10B is an illustration of instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodiment ofFIG. 10A. As can be seen from FIG. 10B, the average efficiencyillustrated by plot 1008 ranges between 29% and 33%. Plot 1010illustrates the instantaneous efficiency of the leading face of therotor blades of the embodiment of FIG. 10A. Plot 1012 illustrates theinstantaneous efficiency of the trailing face of the rotor blades.Average efficiencies are calculated in the manner described above.

FIG. 11 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity for the embodimentof FIG. 10A. FIG. 11 provides a good visual manner of disclosing theoperation of the embodiment of FIG. 10A.

FIG. 12A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for the embodiment of thecross-flow wind turbine that is illustrated in FIG. 12A. Stationaryshaft 1202 is a kidney bean shaped stationary shaft that forms a largegap during certain portions of the rotational cycle of the rotor bladesaround the stationary shaft 1202. As can be seen from FIG. 12A, a fairlylarge low pressure vortex is formed on the trailing face of the rotorsduring the return cycle.

FIG. 12B is an illustration of the instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodimentillustrated in FIG. 12A. As can be seen from FIG. 12B, the averageefficiency that is illustrated by plot 1206 ranges between 28% and 30%.The instantaneous efficiency of the leading face of the rotor blades isillustrated by plot 1208. The instantaneous efficiency of the trailingface of the rotor blades is illustrated by plot 1210. The averageefficiency illustrated by plot 1206 is calculated in the mannerdescribed above.

FIG. 13 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity for the embodimentillustrated in FIG. 12A. The diagram of FIG. 13 illustrates the mannerin which the vortex 1202 is formed.

FIG. 14A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for the embodiment of across-flow wind turbine illustrated in FIG. 14A. The embodiment of FIG.14A uses a kidney shaped stationary shaft 1402 that is similar to thekidney shaped stationary shaft 1202 of the embodiment of FIG. 12A, butstationary shaft 1402 is positioned so that a gap is formed during adifferent portion of the rotational cycle. Again, a vortex 1404 isformed near the trailing face of the rotor blades during the returncycle.

FIG. 14B is a illustration of the instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodimentillustrated in FIG. 14A. As can be seen from FIG. 14B, the averageefficiency illustrated by plot 1406 ranges between 27% and 32%. Plot1408 illustrates the instantaneous efficiency of the leading face of therotor blades of the embodiment of FIG. 14A. Plot 1410 illustrates theinstantaneous efficiency of the trailing face of the rotor blades.

FIG. 15 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity for the embodimentof FIG. 14A. FIG. 15 illustrates the flow patterns and intensities thatallows a visual interpretation of the manner of operation of thecross-flow wind turbine illustrated in FIG. 14A.

FIG. 16A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for an embodiment of across-flow wind turbine that is illustrated in FIG. 16A. FIG. 16A issimilar to the embodiment of FIG. 12A, except that FIG. 16A uses akidney bean shaped stationary shaft 1602 that is larger than stationaryshaft 1202 of FIG. 12A. The larger shaft reduces the size of the rotorblades and provides a larger gap between the shaft and the rotor blades.The result is a large vortex 1604 that creates a large negative pressurearea on the trailing face of the rotor blades during the return portionof the rotational cycle.

FIG. 16B is an illustration of instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodimentillustrated in FIG. 16A. As can be seen from FIG. 16B, the averageefficiency, illustrated by plot 1606, ranges between 24% and 26%. Plot1608 illustrates the instantaneous efficiency of the leading face of therotor blades of the embodiment illustrated in FIG. 16A. Plot 1610illustrates the instantaneous efficiency of the trailing face of therotor blades.

FIG. 17 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity for the embodimentillustrated in FIG. 16A. FIG. 17 provides a good visual interpretationof the operation of the embodiment of FIG. 16A.

FIG. 18A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for the embodiment of across-flow wind turbine that is illustrated in FIG. 18A. The rotorblades illustrated in FIG. 18A have a J-shaped pattern rather than thesemi-circular 120° arc pattern used in other embodiments disclosedherein. Shaft 1802 is a rotating shaft that is connected to the rotorblades of the embodiment illustrated in FIG. 18A.

FIG. 18B is an illustration of the instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodimentillustrated in FIG. 18A. As can be seen from FIG. 18B, the averageefficiency illustrated by plot 1804 ranges between 27% and 34%. Plot1806 illustrates the instantaneous efficiency of the leading face of therotor blades of the embodiment of FIG. 18A. Plot 1808 illustrates theinstantaneous efficiency that is calculated for the trailing face of therotor blades using the methods described above.

FIG. 19 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity for the embodimentillustrated in FIG. 18A. FIG. 19 provides a good visual interpretationof the operation of the embodiment of the cross-flow wind turbineillustrated in FIG. 18A.

FIG. 20A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for the embodiment of across-flow wind turbine that is illustrated in FIG. 20A. As shown inFIG. 20A, the rotor blades are arranged in a reverse offsetconfiguration so that a gap is formed between the rotor blades. Thissimulation shows the creation of a vortex 2002 that is located morecentrally on the trailing face of the rotor blades during the returncycle. The negative pressure area 2004 formed between the rotor bladeand the air foil during the power stroke is much smaller than thenegative pressure areas in other embodiments disclosed herein.

FIG. 20B is an illustration of instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodimentillustrated in FIG. 20A. As can be seen from FIG. 20B, the averageefficiency illustrated by plot 2006 ranges between 25% and 26%. Plot2008 illustrates the instantaneous efficiency of the leading face of therotor blades of the embodiment of FIG. 20A. Plot 2010 illustrates theinstantaneous efficiency of the trailing face of the rotor blades. As isapparent from FIG. 20B, the smaller negative pressure area during thepower stroke results in much lower efficiencies in the embodiment ofFIG. 20A.

FIG. 21 is a wind velocity and directional flow diagram that illustratethe direction and flow of the wind and its intensity for the embodimentof FIG. 20A. FIG. 21 provides a good visual indication of the operationof the embodiment of FIG. 20A.

FIG. 22A illustrates pressure gradients calculated by computersimulations using computational fluid dynamics for an embodiment of thecross-flow wind turbine that is illustrated in FIG. 22A. The embodimentof FIG. 22A uses a split rotor blade and a small rotating shaft.

FIG. 22B is an illustration of instantaneous efficiency and averageefficiency of a single rotor blade versus time for the embodiment ofFIG. 22A. As can be seen from FIG. 22B, the average efficiencyillustrated by plot 2202 ranges between 23% and 24%. Plot 2204illustrates the calculated instantaneous efficiency of the leading faceof the rotor blades of the embodiment of FIG. 22A. Plot 2206 illustratesthe instantaneous efficiency calculated for the trailing face of therotor blades. Efficiencies are calculated in the manner described above.

FIG. 23 is a wind velocity and directional flow diagram that illustratesthe direction of flow of the wind and its intensity for the embodimentof FIG. 22A. FIG. 23 provides a good visual interpretation of the mannerof operation of the embodiment illustrated in FIG. 22A.

FIG. 24 is a schematic illustration of the manner in which theembodiment of FIG. 1A can be constructed. Air foil stator 102 can beformed by using pipes 140, 142 and 144 to provide structural support. Abraced framework 146 can be formed between pipe 142 and 144 to addfurther structural rigidity. The skin 148 of the air foil stator 102 canbe formed from sheet metal, or any other desired material and can belaser cut to the desired shape shown in FIG. 24. Sheet metal havingthicknesses of 14 gauge or 16 gauge, such as used in car fenders, can beemployed to provide the desired shape. Other materials can also be usedsuch as light weight laminates. Similarly, stator 104 can be formed bypipes 150 and 152 with standard braced framework that is covered with asheet metal skin. Stator 106 can include pipes 154, 156 to form astructural member in the same manner as described above. Stators 102,104, 106 may also be constructed from pre-cast concrete forms, or castin place concrete forms, or any other construction technique known inthe art.

FIG. 25 is an isometric view of the embodiment illustrated in FIG. 24without a top lid. A low base member 2502 may be provided to directground winds into the device. This low base member is not a requiredelement of the embodiment illustrated in FIG. 25 and can be replacedwith simply a flat base plate.

FIG. 26 is an isometric view of the embodiment of FIG. 25 that is viewedfrom a different direction. Again, the embodiment of FIG. 26 is shownwithout a top plate.

FIG. 27 is an isometric view of the manner in which the rotor blades canbe constructed. As shown in FIG. 27, ribs 2702, 2704, 2706 and 2708provide structural rigidity and the desired shape of each of the rotorblades. A braced framework (not shown) can be provided between each ofthe ribs 2702-2708. Skin 2710 is then applied to the surface of thebraced framework to form the leading and trailing faces of the rotorblades. Rotating shaft 2712 is connected to each of the ribs 2702-2708and to the skin 2710. The skin 2710 may be constructed from metal,aluminum, composites, or any other material known in the art.

FIG. 28 is a schematic illustration of one embodiment of a powergeneration plant that can be used with any of the embodiments disclosedherein. As shown in FIG. 28, a rotating shaft 2712 is connected to aright-angle gear box 2702. Rotational energy is transferred in ahorizontal direction to the variable speed gear box 2804. Generator 2806then generates electrical energy from the mechanical energy of thevariable speed gear box 2804.

FIG. 29 illustrates the manner in which the generator 2806 can beconnected directly to the rotating shaft 2712. This direct connection ina vertical manner eliminates mechanical losses resulting from the rightangle gear box 2802 and the variable speed gear box 2804. The rotatingshaft 2712 may also be directly connected to a direct drive generator.This configuration eliminates any mechanical losses from the gearbox byeliminating the gearbox altogether. Various electrical techniques, knownin the art, can be used to generate a 60-cycle signal that can beapplied to the electrical grid.

The present invention therefore provides a cross-flow wind turbine thatis capable of achieving high efficiencies and is operable in low-level,mid-level and high-level wind conditions. Because of the highefficiencies that can be achieved over a wide range of wind speeds, theoverall efficiency of the embodiments disclosed herein are substantiallygreater than the overall efficiencies of axial-flow wind turbines.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andother modifications and variations may be possible in light of the aboveteachings. The embodiment was chosen and described in order to bestexplain the principles of the invention and its practical application tothereby enable others skilled in the art to best utilize the inventionin various embodiments and various modifications as are suited to theparticular use contemplated. It is intended that the appended claims beconstrued to include other alternative embodiments of the inventionexcept insofar as limited by the prior art.

1. A method of capturing wind energy using a cross-flow wind turbinecomprising: generating a low pressure area on a leading face of a rotorblade by accelerating the flow of air across the surface of an airfoilstator that is positioned to form a predetermined gap between said rotorblade and said air foil stator during a power stroke of said rotorblade; using a blocking stator to substantially block wind from impedingmovement of said rotor blade during a return cycle of said rotor bladeand directing said substantially blocked wind to a trailing face of saidrotor during said power stroke of said rotor blade so as to create apressure differential between said leading face and said rotor blade andsaid trailing face of said rotor blade during said power stroke thatcreates a force that rotates said rotor blade.
 2. A cross-flow windturbine system that is capable of capturing wind energy comprising: arotor having at least two semicircular shaped rotor blades; an airfoilstator positioned to capture and accelerate wind across an airfoilsurface of said airfoil stator and provide a gap having a predeterminedsize between said rotor blades and said airfoil surface so that anegative pressure area is formed on a leading face of said rotor bladesas said rotor blades pass by said airfoil surface during a power stroke;and a blocking stator positioned to substantially block wind fromimpeding upon said leading face of said rotor blades during a returnstroke and direct wind that is blocked by said blocking stator onto atrailing face of said rotor blades during said power stroke such that apressure differential is created between said leading face of said rotorblades and said trailing face of said rotor blades during said powerstroke that creates a force that rotates said rotor blade.
 3. Across-flow wind turbine that generates mechanical energy from windcomprising: a rotor having a plurality of rotor blades that aresubstantially symmetrically disposed around a rotor; a rotor spaceformed in a volume that is swept out by said rotor blades, said rotorspace having a drive portion in which said rotor blades are driven bysaid wind and a return portion in which said rotor blades return to saiddrive portion; a plurality of stators that direct wind into said driveportion and direct wind away from said return portion to cause saidrotor to turn and generate said mechanical energy, said stators beingplaced around said rotor to provide a substantially bidirectionalcross-flow turbine.
 4. The cross-flow turbine of claim 3 wherein saidrotor axis is vertical and said stators extend at least partially over abase so that said base and said stators capture wind along lowerportions of said cross-flow turbine and direct winds from said lowerportion of said cross-flow turbine.
 5. A method of generating mechanicalenergy from wind comprising: providing a cross-flow wind turbine havingstators and a rotor that sweeps out a rotor space, said rotor spacehaving a drive portion and a return portion; placing a plurality ofrotor blades substantially symmetrically around said rotor; placing saidstators around said rotor in locations that substantially direct saidwind into said drive portion of said rotor space so that said winddrives said rotor blades in said drive portion, and substantially blocksaid wind from entering said return portion of said rotor space so thatsaid rotor blades return to said drive portion to generate saidmechanical energy.
 6. The method of claim 5 wherein said process ofplacing said stators around said rotor further comprises: placing atleast one stator in a position to block said wind from entering saidsecond portion whenever said wind flows substantially from a firstpredetermined direction, and placing at least one other stator in aposition to direct said wind into said first portion whenever said windis flowing substantially from said first predetermined direction.
 7. Themethod of claim 5 wherein said process of placing said stators aroundsaid rotor, further comprises: placing at least one stator in a positionto block said wind from entering said second portion whenever said windflows substantially from a first and a second predetermined direction,and placing at least one other stator in a position to direct said windinto said first portion whenever said wind is flowing substantially fromsaid first and said second predetermined direction.
 8. The method ofclaim 5 wherein: providing a cross-flow turbine comprises providing avertical cross-flow turbine; and, placing said stators comprises placingsaid stators so that said stators at least partially extend over a baseso that a utility enclosure and said stators direct wind from lowerportions of said cross-flow turbine into said cross-flow turbine.
 9. Amethod of capturing wind energy using a cross-flow wind turbinecomprising: providing an airfoil stator that is positioned to captureand accelerate wind across an airfoil surface of said airfoil stator;generating a low pressure area on a leading face of a rotor blade bypositioning said airfoil stator to form a predetermined gap between saidrotor blade and said airfoil stator, said low pressure area generating aforce on said leading face of said rotor blade that rotates said rotorblade in an efficient manner.
 10. A cross-flow wind turbine system thatis capable of capturing wind energy comprising: a rotor having at leasttwo semicircular shaped rotor blades; an airfoil stator positioned tocapture and accelerate wind across an airfoil surface of said airfoilstator and provide a gap having a predetermined size between said rotorblades and said airfoil surface so that a negative pressure area isformed on a leading face of said rotor blades as said rotor blades passby said airfoil surface that creates a force that rotates said rotorblades.